Physics Paper 2

• Sound waves are an example of longitudinal waves.
• CONTACT FORCE: when objects are physically touching eg. reaction force, friction, tension.

  NON-CONTACT FORCE: without objects physically touching eg magnetism, electrostatic force and gravity a VECTOR is a quantity with MAGNITUDE & DIRECTION. a SCALAR is a quantity with MAGNITUDE only.
• here, gravitational field strength is 9.8N/g. that means every 1kg has a weight of 100.

  WORK DONE just means energy transferred by a force. this means that if you hold an object or lift at A CONSTANT

  speed, you must be pushing upwards with a force that's the same size as its weight!
• any object that deforms ELASTICALLY (returns to its original shape) obeys HOOKE'S LAW

  force is directly proportional to extension.

  gradient = spring

  constant.

  PRACTICAL:

  add masses onto spring to change force.

  • measure extension with ruler at each weight, plot f against e.
  • gradient of graph = spring constant.
  • avoid systematic error by lining up 0cm with bottom of spring.
  • avoid parallax error by getting on eye level when measuring
• the GRADIENT of a DISTANCE/DISPLACEMENT-

  TIME graph gives you

  the SPEED/VELOCITY.
• the gradient of a SPEED/VELOCITY - TIME graph is ACCELERATION

  while the area under the graph gives you DISPLACEMENT.
• NEWTON'S 1st LAW: if no resultant force acts on an object, its motion will be constant (velocity will not change).

  NEWTON'S 2nd LAW: F= ma

  NEWTON'S 3rd LAW: for every action (force), there is an equal and apposite reaction (force).
• F= ma PRACTICAL:

  • accelerate the trolley on track with slotted mass on string over pulley.
  • use lightgate to measure acceleration.
  • change force by removing masses and placing on trolley to keep total mass the same.
  • use f= ma.
• STOPPING DISTANCE = THINKING + BRAKING.

  THINKING DISTANCE is affected by;

  • speed (proportional)
  • distractions
  • alcohol
  • alcohol
  • tiredness

  STOPPING DISTANCE

  is affected by:

  • speed
  • condition of brakes, tires and road
  • weather conditions
• momentum= mass x velocity

  in any collision, TOTAL MOMENTUM iS ALWAYS CONSERVED.

  TYPES:

  • rebound

  • coupling

  • recoil
• WAVES

  transfer ENERGY without transferring MATTER

  LONGITUDINAL WAVES: direction of oscillation is PARALLEL with the direction of energy transfer (eg sound, seismic). consists of COMPRESSIONS AND REFRACTIONS

  TRANSVERSE WAVES: the direction of oscillation is PERPENDICULAR with the direction of energy transfer (eg water, light, EM).
• WAVES PRACTICALS

  SOUND

  • someone makes a noise whilst standing within proximity of a wall. another person starts a stopwatch when they hear it, stopping it when the sound echoes and they hear it again.
• • LIQUID
  • ripple tank, light above, paper below. motor-powered dipper on the surface.
  • take photos/videos to measure frequency and wavelength.
  • change motor speed and repeat.
• SOLID

  • attatch string to a vibrator /energy generator, pulling it tout with a ramp and adding masses to the end.
  • measure wavelength with a metre ruler.
  • frequency changed by adjusting generator, adjust tension by changing masses (depends what you’re investigating)
  • put into equation.
• all EM waves are EMITTED and ABSORBED by ELECTRONS

  except for gamma. they’re emitted by nuclei
• if the ENERGY of the wave is high enough it can cause an electron to leave its atom leaving an ion. UV and GAMMA are worst
• RADIO WAVES

  phone, wifi

  MICRO WAVES

  cooking, absorbed by H2O

  INFARED

  cooking, absorbed by surface

  VISIBLE LIGHT

  vision

  ULTRAVIOLET

  tanning, can cause cancer

  X RAYS

  medical scans, dangerous

  GAMMA RAYS

  sterilisation, medicine, dangerous
• PRACTICAL:

  show that MATTE BLACK is the best emitter and absorber of IR: use LESLIE CUBE with THERMOMETER or tubes wrapped in different materials under the source .eg. IR lamp. SHINY materials are the WORST emitters and absorbers
• When waves enter a new MEDIUM (material) their SPEED changes, as does their ANGLE.
• if SPEED decreases, WAVELENGTH does, whilst FREQUENCY remains constant. we only need to draw the RAYS, not the WAVEFRONTS
• if the wave slows down, it bends towards the NORMAL (eg going from air into another material)
• the angle of REFRACTION is SMALLER than the angle of INCEDENCE
• when the light exits, it speeds up again and bends AWAY from the NORMAL
• PERMANENT magnets always produce a magnetic field whereas INDUCED magnets become magnetised when in another magnetic field.
• mini compasses or iron filings can be put in a magnetic field to visualise it. we always draw the field lines going from North to South pole.
• IRON, COBALT and NICKEL are magnetic (can become induced magnets) and so are attracted

  to permanent magnets. Other metals aren't.
• a CURRENT CARRYING wire in a MAGNETIC FIELD will experience a force (as it produces its own magnetic field that will interact with the other).
• PRACTICAL

  FINDING MAGNETIC FLUX DENSITY

  • place magnet on balance.
  • tare balance, measure mass when known current flowing.
  • convert to newtons.
  • measure lenath of wire in field.
  • rearrange f=BIL to calculate B.

  right hand rule= current in wire.

  left hand rule = direction of force.
• motors use the motor effect, both sides of a coil experience a force in opposite directions, and it turns.
• TO INCREASE SPEED (motor effect):

  •add more turns to the coil

  • increase voltage/current

  • use a stronger magnet
• a SPLIT RING COMMUNICATOR is used to ensure that the current is reversed every half turn to keep the coil spinning
• LOUDSPEAKERS use the motor effect:

  a current is sent from the source, causing the COIL and SPEAKER CONE to vibrate, sending sound waves